Conventionally, a circularly polarizing plate has been provided to an organic electroluminescent display device (hereinafter, may be appropriately referred to as an “organic EL display device”) and a liquid crystal display device for reducing reflection of outside light on a display surface in some cases. In general, a film obtained by combining a polarizing film and a λ/4 plate is used as such a circularly polarizing plate. However, most of conventional λ/4 plates were actually capable of achieving a phase difference of an approximately quarter wavelength only with light in a specific narrow wavelength range. Therefore, although reflection of outside light in a specific narrow wavelength range can be reduced by the circularly polarizing plate, reduction of reflection of other outside light was insufficient.
To deal with this issue, a broadband λ/4 plate obtained by combining a λ/4 plate and a λ/2 plate has been recently proposed (see Patent Literatures 1 to 4). With the broadband λ/4 plate, a phase difference of an approximately quarter wavelength for light in a wide wavelength range can be achieved. Therefore, a circularly polarizing plate that can reduce reflection of outside light in a wide wavelength range can be achieved.